1. Field of the Invention
The present invention relates to a method for manufacturing a nitride-base semiconductor element and a nitride-base semiconductor element.
2. Description of the Related Art
Recently, nitride-base compound semiconductors (e.g., GaN, InN, AlN) have been frequently used as materials for light-emitting elements (e.g., blue and green light-emitting diodes (LED), blue-violet semiconductor laser) and electronic devices (e.g., high-speed transistors that can be operated with a high temperature). This nitride-base semiconductor is generally formed on a growth substrate of sapphire or SiC by the heteroepitaxial growth method because the manufacture of bulk single crystals is difficult.
However, sapphire, which is insulating material, has caused a problem in which p and n electrodes must be formed on a single surface to reduce the number of elements that can be obtained from a wafer having the same diameter, to reduce an effective light emitting area in a single area of an element, and to cause difficulty in cleavage in order to prepare cavity facets required for laser. Furthermore, a sapphire substrate has a thermal conductivity of 42 W/m·k that is lower than a thermal conductivity of 130 W/m·k of GaN. Thus, a nitride semiconductor element formed on the sapphire substrate had a poor heat radiation performance.
To solve this, a method has been suggested by which a surface of a nitride-base semiconductor element layer is joined with a support substrate by thermocompression or the like to separate a growth substrate of sapphire or the like from the support substrate and the nitride-base semiconductor element layer. Such separation methods have been disclosed, for example, by a method for polishing a growth substrate to separate a nitride-base semiconductor element substrate (see Japanese Patent Unexamined Publication No. 2004-266240 for example) and a method for emitting laser light from a back face of a growth substrate to separate the growth substrate (see Japanese Patent Unexamined Publication No. 2000-101139 for example).
However, the separation method by polishing as described above provides a poor throughput and may cause an abnormal crack in the polishing and thus the reuse of a growth substrate is difficult. The separation method by laser emission as described above on the other hand needs to appropriately maintain a laser light wavelength and a band gap between a nitride-base semiconductor element layer and a growth substrate. Thus, this method is not versatile to different types of growth substrates and thus requires laser apparatuses having appropriate wavelengths respectively, which is not economic.